write to log-file immediatly on every log

[jcpvdm]

This helps tracking current state of events when running bngblaster in the background like this:
bngblaster -L log -C blaster.json &> /dev/null &

Before this patch, logs were buffered and not written immediately.

[hannesgredler]

I'd rather not do this as it will kill performance for hot logging environments. What i'd do instead is to start a periodic timer (100ms) that calls into fflush(); That way you can tune how much delay you want to accept.

[jcpvdm]

sounds good @hannesgredler. Perhaps this PR can be closed and you add a commit using the timer method?

[jcpvdm]

@hannesgredler, I have redone it using timer following your suggestion, can you have a look?

[hannesgredler]

Looks good - very nice !